To get you started self-publishing in multiple formats!
10 ISBN Most publishers these days are going to publish at least five (5) versions of a book (Hardback, Softback, EPUB, MOBI, and PDF), each of which requires an ISBN. Owning a block of 10 ISBNs is usually enough for two different books. Those who purchase blocks of 10 ISBNs are usually self publishers who have researched their needs before making a purchase and realise this is the most cost effective purchase for their needs. The price of 10 ISBNs is $88